Pump Piston Device

ABSTRACT

A pump piston device is for reciprocating movement in a pump cylinder. Between the pump piston and the pump cylinder, an annular space is formed which is defined by a first seal and a second seal, the annular space being pressurized, and the first seal and the second seal being in a common piece of material which constitutes the pump piston.

This invention relates to a pump piston. More particularly, it relatesto a pump piston for reciprocating movement in a pump cylinder in which,between the pump piston and the pump cylinder, an annular space isformed which is defined by a first seal and a second seal, the annularspace being pressurized.

In piston pumps working with particle-containing or non-lubricatingfluids, seal wear may be a considerable problem, in particular in thecase of high pressures.

According to the prior art, it is sought to relieve the problem byarranging scrapers or several successive seals, for example, around thepiston.

WO document 2005/080836 discloses a pump in which the piston is providedwith two seals with an intermediate annular space.

U.S. Pat. No. 5,701,797 and EP patent application 1975409 deal withpumps in which there are two seals arranged in the cylinder pipe.

NO patent 321183 discloses a piston in which, on a portion of theexternal jacket surface of the piston facing the pressure side of thepiston, an axially movable sleeve is formed, sealing against the piston.Externally, the piston and the sleeve are each provided with arespective seal sealing against the cylinder wall. The area between theexternal seals of the piston and the sleeve is pressurized by means of afluid. During the pump stroke, the piston and the sleeve are movedtowards the fluid which is to be pumped. The sleeve is thereby movedsomewhat along the piston, so that pressure builds up between the twoseals. The sleeve is of such a design that the pressure is approximatelythe same on both sides of the seal surrounding the sleeve. The movementof the sleeve on the piston and the relatively large cross-sectionalarea of the sleeve reduce the volumetric efficiency of the pump.

The invention has for its object to remedy or reduce at least one of thedrawbacks of the prior art.

The object is achieved according to the invention through the featureswhich are specified in the description below and in the claims thatfollow.

A pump piston is provided for reciprocating movement in a pump cylinderin which, between the pump piston and the pump cylinder, an annularspace is formed, defined by a first seal and a second seal, the annularspace being pressurized and the first seal and the second seal being ina common piece of material which constitutes the pump piston. The pumppiston is characterized by a compensation piston being movable in acompensation cylinder in the pump piston, the compensation pistoncommunicating, by its first end portion, with the pressure side of thepump piston, and, at its second end portion, with the annular space viaa piston channel.

Thus, it is possible to form the piston in a simple way, as the firstseal and the second seal can be arranged in a common piece of material.

The pump piston may be crank-operated or moved in other known ways, forexample hydraulically or pneumatically.

A shoulder may prevent the compensation piston from being moved out ofthe compensation cylinder.

The annular space may be supplied with pressure fluid via a check valveand a cylinder channel. The pressure fluid may thereby be supplied tothe annular space at a considerably lower pressure than the operatingpressure of the piston pump, as the check valve will close to the returnflow of pressure fluid during the working stroke of the piston pump.

The operation of the pump piston is described in the characterizing partof the application.

A pump piston in accordance with the invention exhibits the advantageousfeatures from NO 321183 with respect to seal life, with just aninsignificant reduction in the volumetric efficiency.

In what follows is described an example of a preferred embodiment whichis visualized in the accompanying drawings, in which:

FIG. 1 shows schematically a piston pump which is provided with a pumppiston in accordance with the invention, the piston being moved in itssuction stroke; and

FIG. 2 shows schematically the same as FIG. 1 but during the workingstroke of the piston pump.

In the drawings, the reference numeral 1 indicates a piston pumpcomprising a pump casing 2 with a pump cylinder 4, a crankcase 6 and avalve block 8 for the medium which is to be pumped.

A driven crank 10 is supported in the crankcase 6 and connected, in amanner known per se, to a pump piston 12 by means of a crank rod 14. Thepump piston 12 is reciprocatable in the pump cylinder 4.

The valve block 8 is formed with an inlet valve 16 and an outlet valve18.

The pump piston 12 is provided with a first surrounding seal 20 which isrelatively close to its pressure side 22, and a second surrounding seal24 on the crank side of the first seal 20.

An annular space 26 is defined by the pump cylinder 4, the pump piston12 and the seals 20, 24.

A compensation cylinder 28 has been bored into the pump piston 12 fromthe pressure side 22 of the pump piston 12. A compensation piston 30 issealingly and movably arranged in the compensation cylinder 28, acompensation piston chamber 32 being defined by the compensationcylinder 28 and the compensation piston 30. The compensation pistonchamber 32 communicates with the annular space 26 via a piston channel34.

A shoulder 36 prevents the compensation piston 30 from being moved outof the compensation cylinder 28. A supporting spring 38 may be arrangedin the compensation piston chamber 32 and be arranged to move thecompensation piston 30 in the direction towards the shoulder 36.

A feed pump 40 supplies the annular space 26 with pressure fluid via apipe 42, a check valve 44 and a cylinder channel 46. The pressure fromthe feed pump 40 is restricted by an overpressure valve 48.

During operation, the annular space 26 is filled with a preferablylubricating pressure fluid by the feed pump 40 via the pipe 42, thecheck valve 44 and the cylinder channel 46. An appropriate maximumpressure, which may be relatively low in relation to the maximumpressure of the piston pump 1, has been set on the overpressure valve48.

Pressure fluid flows from the annular space 26 via the piston channel 34into the compensation piston chamber 32, whereby the compensation piston30 is moved until it hits the shoulder 36.

During the suction stroke of the piston pump 1, see FIG. 1, the pumppiston 12 is moved in the direction towards the crank 10, the inletvalve 16 opens and pumped liquid enters the piston pump 1. Thecompensation piston 30 stays in its position, bearing against theshoulder 36, because of the pressure in the compensation piston chamber32 and a possible underpressure in the piston pump 1.

When the piston pump 1 starts its pump stroke, see FIG. 2, the inletvalve 16 closes, whereby the pressure in the piston pump 1 increasesuntil the outlet valve 18 opens. The increased pressure in the pistonpump 1 works against the compensation piston 30 which is moved inwardsin the compensation cylinder 28. The pressure in the compensation pistonchamber 32 increases by the check valve 44 closing. The annular space 26thereby gets the same pressure as the piston pump 1.

Thus, during the pressure stroke of the piston pump 1, there isapproximately the same pressure on both sides of the first seal 20,which substantially reduces seal wear, even when pumping particle-ladenliquid.

The second seal 24, sealing against a clean lubricating fluid, receivesfull pumping pressure.

1. A pump piston device for reciprocating movement in a pump cylinder inwhich there is formed, between the pump piston and the pump cylinder, anannular space which is defined by a first seal and a second seal, theannular space being pressurized, and the first seal and the second sealbeing in a common piece of material which constitutes the pump piston,wherein a compensation piston is movable in a compensation cylinder inthe pump piston, the compensation piston communicating, by its first endportion, with the pressure side of the pump piston, and, at its secondend portion, with the annular space via a piston channel.
 2. The devicein accordance with claim 1, wherein the annular space is supplied withpressure fluid via a check valve and a cylinder channel.